It is known that certain synthetic resins can be used to form moldable materials which display useful optical properties. The use of such resins for making optical lenses has increased rapidly in recent years due to the advantages plastic lenses have over glass lenses, e.g. resistance to breakage and reduced weight.
Plastic lenses have generally been prepared by injection molding or other techniques requiring melting of the resin. However, these techniques are suitable for heat-stable resins only. Such resins do not always exhibit acceptable optical properties, e.g. high refractive index and optical clarity. Other resins, which have potentially-desirable optical properties, lack poor stability and can be injection molded over only a narrow temperature range, if at all.
It is desirable, therefore, to have fabrication methods which would not require melting of the resin. One possibility would be to cast a lens from a solution of a resin in organic solvent. However, conventional solvent-based formulations cure too slowly due to slow solvent evaporation, and exhibit bubble entrapment and unpredictable lens shrinkage. Obviously, slow curing formulations cannot be used in high speed manufacturing operations. Bubble entrapment and lens shrinkage result in unacceptable optical qualities.